The filling of small tanks with liquids has long been a source of inventive ideas, particularly as small gasoline motors and kerosene heaters have proliferated. Inventions of many types have resulted.
Funnels have been designed with almost every type of signal to indicate when the tank is full. Some devices require the small vessel containing the source liquid to be equipped with special spouts. Some spouts have a mechanical trip valve at the end which rests on the mouth of the tank to be filled, with the operator moving the source liquid tank to open or close the trip valve, making such decision by observing the liquid level through the tank opening. A common problem with the valved spouts is visually seeing the liquid level inside the tank so as to know when to stop pouring. Frequently, the first indication of being "filled" is also an overflow.
Some have spouts which contain two passages, one for liquid being poured, the other for the return air, and the dual passage spout is inserted into the to-be-filled tank's opening. When the liquid level therein rises with filling, the return air vent is covered so that flow characteristics change, and the operator then lowers the source tank to where flow isn't possible.
In a variation of the return air control, a dual passage, transparent connection line is connected to the openings of both the tank to be filled and the source tank. The operator observes the return flow through the transparent connection line and controls the flow by raising or lowering the source tank.
Each of these inventions has had some shortcoming, as none has become a universally accepted solution. A general problem with prior funnel devices has been either their complexity (valves, air passages, etc.) or the funnel's resting in the tank opening which obscures the view of the liquid level in the tank.
It can be observed that, when pouring at normal rates into a funnel, a certain liquid level tends to accumulate in the lower portion of a conical funnel, just above where the liquid enters the throat. This occurs whether the funnel is conical with a round (straight or tapered) throat or is of square, rectangular, ellipsoidal or compound cross section. When the tank below the funnel becomes full, the level in the funnel cone rises higher, indicating to the operator to lower the source tank and cease filling. Almost invariably this has already resulted in overfilling and consequent spillage.
In general, there are two common problems: seeing the liquid level as the tank becomes full and what to do with the "lag time" liquid that invariably occurs between seeing that "full" has occurred and lowering or adjusting the source tank so as to actually cause flow to stop. The "lag time" liquid can represent a substantial amount and is particularly dangerous if it is spilled due to overfilling. In addition, it is desirable to not solidly connect the to-be-filled tank to the source tank, both because of the physical constraints and because of potential leak sources created during filling.
Accordingly, it is desirable to have a funnel to introduce the filling liquid into the mouth of the to-be-filled tank, allowing free-flow from the source tank (or its nozzle). It is also desirable to provide an easily visible level indication when a "full" condition has been reached. It is further desirable to provide a method of accepting a "lag time" apparent overfill without a resultant spill no matter what specific type of spout is used. It is still further desirable that such overfill method control be independent of the shape of the tank to be filled (i.e. if an air gap is created in the tank by the location of the return air vent in a sealably engaged funnel device, the air gap can easily vary in volume depending on the shape and/or orientation of the tank).